1. Field of Invention
The present invention relates to a cylindrical filter for a gas generator for use in a restraining apparatus and the like, and also to a gas generator using the cylindrical filter.
2. Description of Related Art
A gas generator that uses a solid gas generating agent uses a filter to cool a combustion gas and collect combustion residues. While known filters include those in which a metallic mesh or wires are woven in many layers and then compression-molded and those in which wires are wound in many layers, when the used gas generating agent generates a low-temperature combustion gas or produces only a small amount of combustion residues, filters that are lighter than those described above can be used instead.
JP-A No. 2000-198409 discloses an example in which expanded metal is molded into a cylindrical body and used as a filter. In a gas generator shown in FIG. 1, a combustion chamber 22 is formed inside a housing 3. A gas generating agent 6 and a filter 7 are arranged inside the combustion chamber 22. The filter 7 is cylindrically formed by winding expanded metal in many layers. An upper end of the filter 7 is in contact with a diffuser shell 1, and a lower end thereof is in contact with a closure shell 2.
In particular, a cushion 50 is disposed on an upper end surface 28 of the filter 7. The cushion 50 prevents short-passing of combustion gas between the filter 7 and the diffuser shell 1.
Further, JP-A No. 2001-301561 discloses a filter using a layer material with different specifications for each layer. In particular, an example shown in FIG. 3 discloses an example of a filter using expanded metals with different pitch ratios for an inner layer and an outer layer.
However, although expanded metal and metal lath are favorable in view of weight reduction, elasticity is low by itself. Therefore, when expanded metal or metal lath is disposed in the gas generator as a filter according to JP-A No. 2000-198409, gaps formed at abutting portions on both ends are less likely to be resolved and a short-passing of combustion gas is more likely to occur. As a result, a cushion member 50 such as that described in JP-A No. 2000-198409 (a cushion member described in paragraph 45 and having a short-passing preventing portion 51) has to be disposed.
FIGS. 2 and 5 and paragraph 46 in JP-A No. 5-213147 describe both ends of layers 154 and 156 which form a filter being folded.
However, the layer 154 is made of a ceramic fiber mat (in paragraph 33) which has, in entirety, a uniform strength and which can be easily folded, and the layer 156 is made of a nickel felt material (in paragraph 33) which has, in entirety, a uniform strength and which can be easily folded.
Claim 8 and paragraph 27 in JP-A No. 2005-193762 describe that, in a three-layer cylindrical filter that is manufactured by winding a metallic wire, a second layer is protruded from an end surface to be squashed and tightly attached when disposing a filter in a gas generator, whereby short-passing is prevented.